1. Field of the Invention
This invention relates to materials handling systems and, more particularly, to storage placement and selection of material within a materials handling system.
2. Description of the Related Art
An enterprise that receives, consumes, transforms or distributes material during the course of its operations may implement a materials handling system to coordinate how material is managed within the enterprise. For example, in a manufacturing context, material may include raw materials, feedstocks, parts, etc. that may arrive at a manufacturing facility for processing as well as intermediate or finished goods resulting from the manufacturing process. Similarly, in a distribution context, retailers, wholesalers and other types of distributors may receive materials such as goods or products and distribute them to clients or customers.
Material may be stored as inventory within an inventory facility and made available for ordering or use by clients or customers. For example, in a manufacturing context, a client may include a step of a manufacturing process that includes a particular type of material as an input, while in a retail context, a client may include a customer who places an order for a product. In conventional materials handling systems, like items often may be stored together within inventory. For example, items having a common Universal Product Code (UPC), Stock-Keeping Unit (SKU) code, or other designation (including proprietary designations) may be stored together within inventory.
When retrieval of material from inventory is necessary, for example in response to a client's order or to replenish a manufacturing process, one or several inventory items must be retrieved or “picked” from inventory and prepared for delivery to the requestor or recipient. In an inventory environment that includes a large number of different items and services the demands of a number of different requesters, at any given time there may be a substantial number of outstanding requests for picking items. To improve picking productivity, a materials handling system may employ multiple item pickers distributed throughout an inventory facility and may assign different picking operations (including, in some cases, picking of different items for a single order) to different pickers.
The productivity of a given picker may generally depend on how many picking operations the given picker may complete per unit of time or effort. For example, if a picker moves a substantial distance between picking two items, the time spent moving without picking may be regarded as unproductive time. Correspondingly, reducing the distance a picker moves between successive picking operations may improve that picker's productivity.
However, a difficulty may arise when storing small quantities of certain inventory items within a relatively large inventory facility. For example, the quantity kept on hand of an item may be proportional to the relative demand for that item. But as the quantity of an item to be stored decreases, so does the number of possible discrete locations within the inventory facility where the item might be stored. For example, if only one indivisible unit of a given item is kept on hand, it cannot be stored in more than one location within the facility. If the facility is large and the given item is randomly placed within it, then it is possible that the given item may be quite far from the nearest picker at a time when the given item is requested to be picked. Thus, some picker may have to move a considerable distance from its current location to retrieve the given item, which may reduce that picker's productivity.